Two senior members of the Senate Foreign Relations Committee have said that Pakistan's powerful intelligence agency ISI was sheltering Taliban fighters along the border, thus undermining the stability of Afghanistan.

The senators - Richard G. Lugar, Republican of Indiana, and Joseph R. Biden Jr., Democrat of Delaware - said they did not believe that President Pervez Musharraf was involved in the destabilizing activities, says New York Times.

But the lawmakers, citing news reports, said there was evidence that ISI might be helping the Taliban and Al Qaeda operatives along the border infiltrate into Afghanistan. The senators also raised concerns that Iran was assisting the warlord Ismail Khan in western Afghanistan.

ISI is "once again either turning a blind eye to or cooperating with" Pashtun groups opposed to the Afghan government of President Hamid Karzai, said Biden, the committee's ranking Democrat, during a hearing on the reconstruction of Afghanistan. The Taliban were composed mainly of Pashtun tribesmen from southern Afghanistan.

Lugar, the committee chairman, said elements of Pakistan's intelligence service, which supported the Taliban in the 1990's, appeared to be trying to gain influence in Afghanistan by allowing Taliban fighters to infiltrate across the border, where they have been attacking Afghan and American soldiers.

"This is international politics impinging on a small country," Lugar said.

Responding to the senators' concerns, two senior administration officials said they thought the situation was not as dangerous as Lugar and Biden had suggested, but they praised Musharraf as a firm ally in the war on terrorism.

But one of the officials, Peter W. Rodman, the assistant secretary of defence for international security affairs, acknowledged that Afghanistan's "neighbouring countries would like to have a hand in it."

During a visit to Washington last week, Pakistan's foreign minister denied the intelligence service was assisting the Taliban. But because of the service's history of close ties with the Taliban, many American officials believe elements of the service have been providing aid to Taliban and Qaeda units operating in the mountains and caves of southeastern Afghanistan, often crossing from the neighbouring tribal areas of Pakistan.

Some American officials, for example, contend that the intelligence service may have provided money, weapons and broadcast equipment to Taliban fighters now in Pakistan to transmit anti-Karzai, anti-American messages into Afghanistan.

But those officials contend it has never been clear whether senior Pakistani intelligence officials are condoning, or even supporting the pro-Taliban activities, or whether such support comes from rogue elements or retired intelligence officers claiming to work for the government.

During the hearing, Republican and Democrat senators urged the administration to support an expansion of the international security unit that now patrols Kabul, so that it can maintain a presence in other Afghan cities.

Afghanistan's ambassador to the United States, Ishaq Shahryar, told the committee that Afghanistan is at the center of a "circle of instability" and that it could not attract foreign investment until security is improved.

"I urge this committee to continue to support the expansion of ISAF," the ambassador said, referring to the 4,600-soldier security unit, known as the International Security Assistance Force.